Organic light emitting diode (OLED) displays are one of hotspots in a field of flat panel display.
Unlike thin film transistor-liquid crystal displays (TFT-LCD) which uses a stable voltage to control brightness, the OLEDs displays are current driven elements and require a stable current to control brightness. The pixel driving circuit of the OLED display comprises a driving tube. When the row in which a pixel unit is positioned is gated, a switching transistor connected to a driving transistor is turned on. Thus, the data voltage is applied to the driving transistor via the switching transistor, enabling the driving transistor to output a current corresponding to the data voltage to the OLED display. Accordingly, the OLED display emits light having a corresponding intensity.